This invention relates generally to apparatus and methods for controllably and accurately dispensing particulate materials, and more particularly concerns reliably dispensing particulate materials from a source container to subsequent unit operation process equipment, for example, receiving receptacles on a fill line conveyor such as toner from a supply hopper through a fill tube to a toner container, or a melt mixing or extruder device.
Currently when dispensing powders, for example, toners into toner containers, toner is transported from the toner supply hopper into the container by, for example, a rotating auger. The auger is a spiral shaped mechanical part which pushes particles of toner inside a fill tube by direct mechanical contact. The nature of this mechanical contact process creates substantial limitations on accuracy and productivity of the toner filling operation. The speed of the toner movement in the fill tube is proportional to the speed of rotation of the auger and is limited by heat release due to auger/toner friction. High auger speeds will generally cause the toner to melt, particularly for low melt toners, such as disclosed in U.S. Pat. No. 5,227,460 to Mahabadi et al., the relevant portions thereof are incorporated herein by reference.
Toner containers typically have a small opening into which the toner is to be added. Furthermore, the toner containers often have irregular shapes to conform to the allotted space within the copying machine. Therefore it becomes difficult to fill the toner container because of the small tube required to fit into the small toner container opening and secondly for all the toner within the container to completely fill the remote portions of the container before the container overflows.
The problems associated with controlling the filling of toner containers are due primarily to the properties of the toner. Toner is the image-forming material in a developer which when deposited by the field of an electrostatic charge becomes the visible record. There are two different types of developing systems known as one-component and two-component systems. In one-component developing systems, the developer material is toner comprised of particles of magnetic material, usually iron, embedded in a black plastic resin. The iron enables the toner to be magnetically charged. In two-component systems, the developer material is comprised of toner of polymer or resin particles and a colorant, and a carrier of roughly spherical particles or beads usually made of steel. An electrostatic charge between the toner and the carrier bead causes the toner to cling to the carrier in the development process. Control of the flow of these small, abrasive and easily charged particles is very difficult. The one-component and two-component systems utilize toner that is very difficult to flow. This is particularly true of the toner used in two component systems. The toner tends to cake and bridge within the hopper. This limits the flow of toner through the small tubes which are required for addition of the toner through the opening of the toner container. Also, this tendency to cake and bridge may cause air gaps to form in the container resulting in incorrect partial filling of the container.
Attempts to improve the flow of toner have also included the use of an external vibrating device to loosen the toner within the hopper. These vibrators are energy intensive, costly and not entirely effective and consistent. Furthermore, they tend to cause the toner to cloud causing dirt to contaminate the ambient air and to accumulate around the filling operation.
Also, difficulties have occurred in quickly starting and stopping the flow of toner from the hopper when filling the container with toner in a high speed production filling operation. An electromagnetic toner valve has been developed as described in the aforementioned commonly owned and assigned U.S. patent application Ser. No. 08/540,993 and U.S. Pat. No. 5,685,348, the disclosures of which are incorporated herein by reference in their entirety. The electromagnetic valve is limited for use with magnetizable toner such as that described for use with one component development systems.